Formation of sheet material using hydroentanglement

ABSTRACT

A method is described for forming reconstituted leather sheet material from a mixture of base fibres, such as leather fibres, and bi-component synthetic fibres which have outer layers which melt at a lower temperature than their inner cores. The fibres are mixed, formed into a web and then heated so that the synthetic fibres fuse together to form a network within the web. The base fibres are then tangled, whilst constrained by the network, preferably using hydroentanglement. A high quality reconstituted leather sheet material is thus produced.

This is a Continuation of U.S. patent application Ser. No. 14/061,058filed Oct. 23, 2013, which is a Continuation of U.S. patent applicationSer. No. 12/767,739 filed Apr. 26, 2010, which is a Divisional patentapplication of application Ser. No. 10/494,475, filed Oct. 29, 2004,which is a US National Stage application of PCT ApplicationPCT/GB02/05381, published as WO 03/048437 filed Nov. 29, 2002 claimingpriority from British Application 0128692.1 filed Nov. 30, 2001, all ofwhich are incorporated by reference.

This invention relates to the formation of sheet material from fibresparticularly using a process known as hydroentanglement or spunlacing.

BACKGROUND

Prior patent application PCT/GB 01/02451 describes the use ofhydroentanglement (or spunlacing) to produce a high qualityreconstituted leather sheet material from waste leather fibres.

A feature of the procedure described in the prior application is the useof specialised screens through which hydroentangling jets are directedat high pressure, in contrast to previously known procedures whereentangling commences at low pressure until the fibres are sufficientlyinterlocked to avoid disruption by the jets. Leather fibres entangleparticularly readily, and with previously known procedures, they form asurface layer of entangled fibres that impedes further entanglement.This is particularly disadvantageous with thick webs needed for leatherproducts but by using the aforesaid screens, jets can penetrate deeplyat high pressure to hydroentangle throughout the depth of the web.

The difficulties with disruption and the formation of a surface layerarise because fibres resulting from the disintegration of waste leatherare far shorter and finer than those normally used for hydroentangling.The screens of the prior patent application provide a means ofconstraining such fibres from being washed away by the jets, but evenwith screens it is difficult to constrain very short fibres such as areproduced by hammer milling waste leather. Also, whatever the length offibres about half the hydroentangling energy is wasted when usingscreens due to the solid parts of the screen shielding significant areaof the web from the jets. The loss of energy when using screens and thelower output rates from using leather fibres of greater length areinherent with the procedure of the prior application.

SUMMARY OF INVENTION

An object of the present invention is to provide a method of entanglingfibres to form sheet material whereby the aforesaid problems arisingfrom use of screens and longer fibres can be avoided or at leastminimised.

According to one aspect of the invention therefore there is provided amethod of forming a sheet material from a mixture of fibres comprisingbase fibres and additional synthetic fibres, said synthetic fibreshaving outer meltable layers, comprising the steps of:

forming the fibres into a web,

heating to melt the outer layers of the additional synthetic fibres soas to cause such fibres to fuse together at intersections to form anetwork within the web,

subjecting the web to entanglement to entangle the base fibres whilstconstrained by the network.

Preferably, the entanglement is hydroentanglement. Preferably also thebase fibres are leather fibres.

Thus, in accordance with a second aspect of the invention there isprovided a method of forming a sheet material from a mixture of fibrescomprising leather base fibres and additional synthetic fibres, saidsynthetic fibres having outer meltable layers comprising the steps of:

forming the fibres into a web,

heating to melt the outer layers of the synthetic fibres so as to causesuch fibres to fuse together at intersections to form a network withinthe web,

subjecting the web to hydroentanglement to entangle the leather fibreswhilst constrained by the network.

The entanglement of the method of the invention is preferably performedusing high pressure jets of liquid (particularly water) preferably inmultiple passes. Reference is made to the prior application for furtherdetails of such features.

In a preferred embodiment, the invention provides a method of formingsheet material with a mixture of leather fibres and man made bicomponentfibres, said bicomponent fibres having outer layers with a lower meltingpoint than the inner cores. The mixture of fibres is formed into a web,which advances through a heating means that melts the outer layers ofthe bicomponent fibres so they fuse at their intersections, and form athree dimensional network throughout the web. Fine jets of water at highpressure are then directed onto the web so they penetrate deeply andhydroentangle the leather fibres while these are constrained by thenetwork of bicomponent fibres.

Fused bicomponent supporting networks are known but not in the contextof the present invention.

Such networks are used in conjunction with wood pulp fibres to impartmost or all of the finished product strength for applications such aswet wipes and absorbent sanitary products. The high pressure jets usedin hydroentanglement would disrupt the bonding of such network and,where such networks are used with hydroentanglement, the bicomponentfibres are fused after hydroentanglement, thereby avoiding suchdisruption. With the present invention the network is used for adifferent purpose to that of providing structural reinforcement for theend product, and entanglement is effected after fusing.

A basic requirement of entangling is that fibres must move in order toentangle, and the fused network would be expected to impede theentanglement of the fibres. Surprisingly, it has been found that leatherfibres can entangle effectively within such networks even if theapparent restraining effects are enhanced by compressing the webscontaining the leather and bicomponent fibres while the surfaces of thebicomponent fibres are still tacky, thereby presenting a significantlydenser layer to the hydroentangling jets.

With the arrangement of the invention, the network can take over part orall of the function of the external screens used in the method of theprior patent application. However, instead of acting on the surface, thenetwork can provide a succession of much lighter screens within thedepth of the web. Each internal screen can have relatively much moreopen area than an external screen, but collectively they can provide aneffective and improved alternative to the external screen of the priorapplication. In particular the network of internal screens allowshydroentangling jets to penetrate deeply at pressures that wouldotherwise disrupt the web.

Apart from replacing the function of the screens, the bicomponentnetwork can also improve the way the leather fibres hydroentangle. Oneof the difficulties of hydroentangling leather fibres is that even whenusing screens they consolidate so readily that they impede drainage ofwater through the web and the resulting flooding can prevent optimumentanglement. However, the three dimensional structure of thebicomponent network can even out the rate of consolidation of the web,which together with the deep penetration can assist the drainage ofwater through the web until full entanglement is achieved.

It is believed that this drainage effect is achieved by thethree-dimensional network of bicomponent fibres providing a resilientrestraint to compaction within the body of leather fibres. It isdesirable to ensure that the network does not hold the leather fibresaway from each other to the extent that there is insufficient proximityfor them to entangle well with each other since this could result in aspongy material less desirable for leather products. This effect can bereduced or prevented by reducing the quantity of bicomponent fibres inthe mix and/or using bicomponents of lower diameter and/or lower elasticmodulus.

In normal hydroentangling practice most of the fibres can start off toofar apart to entangle effectively, and a first pass through the jets isused to bring the fibres close enough to entangle. In a preferredembodiment of the present invention, the fibres are brought into closerproximity before entangling commences by compressing the web containingthe bicomponent network before the fused junctions of the networksolidify. This can more than halve the thickness of the web compared toconventional practice and can effectively eliminate the firsthydroentangling stage used in conventional practice.

In the method of the prior application the external screen helped tocompress the web at the first stage of entanglement, but this can incursignificant loss of hydroentangling energy because of the surface areaof the web being shielded from the jets. However in the presentinvention the solid parts of the internal bicomponent screens can berelatively insubstantial so there can be substantially less shielding ofhydroentangling jets from the fibres. This can reduce the number ofpasses needed by the jets over the web to achieve full entanglement andreduce the energy consumed. Typical production speeds can also increasefrom 6 m/min mentioned in the prior application to over 10 m/min in thepresent invention.

Being relatively fine, the bicomponent network may be less effectivethan externally applied screens for masking the furrows in the surfacecaused by the jets. Accordingly, with the method of the presentinvention external screens may additionally be used (which may begenerally of the kind described in the prior application) in at leastone pass to eliminate or at least reduce or substantially preventformation of surface furrows by the hydro-entanglement jets. In so faras the bicomponent network acts as a series of internal screens,externally applied screens can have more open area than the preferredopenings described in the prior patent application thereby reducing theloss of energy. Such external screens still waste some energy, but theycan be confined to passes where they are needed to mask jet lines.Typically this can be the last pass on the finish face, and possibly thefirst pass so that the jets bite less deeply while the fibres are leastentangled.

The prior patent application describes a method for producing longleather fibres to improve performance of the finished product but suchfibres also pass more slowly through the preferred equipment forair-laying the webs. However with the present invention, short leatherfibres can be used without necessarily adversely affecting productperformance because the network can reduce or eliminate some of thedefects that arise with short leather fibres. For example, products madewith short leather fibres are more liable to surface cracking, but shortbicomponent fibres may still be beneficially used to enhance throughputfrom web laying equipment, as by fusing the bicomponent fibres to form anetwork, they act like much longer fibres and thereby more effectivelyconstrain surface cracking. Short fibres are also more prone to erosionduring hydroentangling, but the network of fused bicomponent fibres canconsiderably reduce this without interfering with the relatively smallmovements needed for hydroentanglement.

Unlike other fields of manufacture where short bicomponent fibres arefused at their intersections, the contribution of bicomponent fibres toprimary strength can be negligible, and the proportion of such fibres inthe total mix can preferably be minimised as they can seriously detractfrom leather-like handle. In cases where the performance of productsmade with short fibres needs to be significantly upgraded this can beachieved by incorporating normal, non-bicomponent fibres with a reducedproportion of bicomponent fibres.

The proportion of bicomponent fibre needed to provide the purely processbenefits of the present invention can be as low as 2% of the totalweight of web, and can be many times less than the percentage used inconventional applications where a bicomponent network is a source ofstrength. Apart from unacceptably increasing stiffness and coarseningthe surface feel of the final product, a bicomponent network thatprovides significant structural contribution may reduce the attachmentof leather fibres to internal reinforcing fabrics by impeding theleather fibres from locking into the interstices of the fabric.

Because of these limitations, in a preferred embodiment of the presentinvention bicomponent fibres are used with weak outer sheaths to promotea partial breakdown of the network as the web progresses throughsuccessive stages of hydroentangling. With each pass the increasedentanglement of the leather fibres can compensate for the reduction ofbonds between bicomponent fibres, and can result in end products withminimal stiffening from the network. Such a procedure would be adisadvantage in conventional practice but, as with the externallyapplied screens of the prior application, the main purpose of thenetwork is to overcome processing problems peculiar to hydroentanglingrather than providing structural strength.

Processing benefits of the bicomponent network also extend to producingthe webs themselves, particularly with commercially available equipmentnormally used for air laying wood pulp fibres. Such processes can havehigh rates of production for short fibres like wood pulp, and thebicomponent network can significantly reduce the erosion of short fibresunder hydroentanglement. This allows short leather fibres such asproduced by hammer milling to be hydroentangled much more effectivelythan by the methods of the prior application.

A further processing advantage of bicomponent networks is that they canprovide sufficient strength to the web before hydroentangling to allowwebs to be wound onto reels at interim stages of production. Thisremoves the need to feed webs directly from the air laying equipment tothe hydroentangling line as in the method of the prior application, andallows the webs to be produced at optimum speeds determined by the airlaying equipment without compromising the operation of thehydroentangling line. Thus, in one embodiment the (or each) web is woundon a reel after formation of the network, and the web is drawn from suchreel to be subjected to said entanglement.

Furthermore, where the product requires two webs on either side of areinforcing fabric, both webs can be formed using one air laying plant.Two reels of webs stabilised with bicomponent networks can then be fedto the hydroentangling line, and can result in a substantial saving ofcapital cost compared to the method of the prior application where twoentire air laying means were required to continuously feed thehydroentangling line. Where a reinforcing fabric is used the base(leather) fibres preferably penetrate this so as to be entangledtherewith.

The fibre content needed to provide adequate reel handling strengthdepends on web thickness, bicomponent content and the strength of themelt-able sheath on the bicomponent fibres. However, generally thepercentage of bicomponent fibre needed to impart sufficient in-processstrength for reel winding need be no more than the same low bicomponentcontent that can provide effective internal screens in the method of thepresent invention. This in-process strength for individual webs is wellbelow the strength after hydroentangling, particularly afterhydroentangling webs and reinforcing fabric to form a final product.

As with most fibrous products, fibre length preferably needs to be aslong as possible. However, long leather fibres produced by textilereclaiming methods have a wide distribution of fibre length from around1 mm to occasionally over 15 mm, and the upper end of the distributioncan cause very slow production rates using air laying equipment designedfor wood pulp fibres. It can therefore be preferable to limit themaximum length of such fibres to around 6 mm, for example by passingthem through a conventional granulating machine (taking care to avoidshortening more than necessary to make a worthwhile improvement in airlaying output). Such methods of shortening fibres can be veryapproximate, but preferably at least 90% of the fibres should be lessthan 6 mm for efficient air laying. Thus, in the method of theinvention, in order to obtain improved throughput from air-layingequipment designed for wood pulp fibres, at least 90% of the base fibreshave a maximum fibre length of 6 mm.

In the case of hammer milled leather fibres there is also a widedistribution of fibre lengths, but lengths are generally much less thanproduced by textile reclaiming methods. Typically the maximum length maybe around 3 mm and, as with fibres produced by textile reclaimingmethods, the average fibre length is significantly less than themaximum. No granulation is required for hammer milled fibres, but themuch shorter length can result in a need to increase average length ofthe mix by adding manmade fibres of predetermined optimum length inorder to improve the physical properties of the final product.

Unlike leather fibres, manmade fibres can be chopped to a constantlength so they can all be of a length that provides the optimum balancebetween air laying throughput and performance of the finished product.For air laying equipment designed for wood pulp, the length of manmadeinclusions may be around 6 mm, but recent improvements in air layingtechnique may make it feasible to increase this to over 10 mm. Theseindicative fibre lengths apply typically to bicomponent andnon-bicomponent manmade fibres in the 1.7 dtex to 3.0 range. Finerfibres can significantly reduce air laying output unless fibre length isreduced appropriately.

Air laying speeds vary considerably depending not only on fibre lengthand diameter, but also on the smoothness and shape of fibres. In theserespects leather fibres are particularly unfavourable regarding airlaying throughput, as they are usually curly and have finely fibrillatedbranches that can impede flow through the perforated distributionscreens of air laying equipment. Air laying rate for un-granulatedleather fibres produced by textile reclaiming methods can be as low as 3m/min for a 200 gsm web, but this can be more than doubled if the fibresare shortened. Laying rates for manmade and pulp fibres can beconsiderably faster.

Regarding the percentage of bicomponent fibre in the mix, it isgenerally preferable to keep this to the minimum as described earlier.The degree to which the bicomponent network compromises leather-likehandle depends on end use, and for shoes the greater stiffness andwearing properties conferred by the bicomponent network can be moreacceptable or even be of benefit compared to (for example) clothingleather. For shoes up to 10% of 3.0 dtex bicomponent can be used, but toobtain better handle it can be preferable to use under 5% bicomponentand a greater proportion of non-bicomponent fibres. In general theoverall range for additional synthetic fibres is 2% to 10% by weightwith a preference towards the lower end of the range.

From the viewpoint of providing effective internal screens, the numberof bicomponent fibres can be as significant as their percentage byweight of total mix. For example, reducing from 3.0 to 1.7 dtex in a 5%mix would proportionately increase the number of fibres in the mix, andto obtain a similar screen effect, the percentage of 1.7 dtex fibres mayneed to reduce to below 3%. Using finer bicomponent fibres can alsoprovide better surface feel to the finished product, which is an addedbenefit.

Commercially available bicomponent fibres are generally not less than1.7 dtex, but end product handle can be improved by choosingbicomponents with a low elastic modulus, such as polypropylene. Theseusually have polyethylene melt-able sheaths that are not particularlystrong but can still provide sufficient reel handling strength even atlow percentage additions. As mentioned earlier some degree of bondweakness can be an advantage for some product applications as this canimprove the handle of the final product. In applications where morestiffness is acceptable or required, stronger bicomponents can be used,such as polyester with nylon sheaths.

Bonding between bicomponent fibres at their intersections can beachieved by passing hot air through the web to melt the outer coatingwhile the fibres are held between porous belts. The bond may not bestrong enough to link short fibres together to contribute significantlyto the tensile strength of the final product, but the bonds may besufficient to provide an effective network for hydroentangling andenough anchorage to resist surface cracking of the finished product.

The fused intersections of the network may be at least partiallydisrupted by the entanglement.

Resistance to surface cracking can be enhanced by including ordinarynon-bicomponent manmade fibres in the mix. Such fibres can alsosignificantly improve peel resistance of the surface coating that isusually applied to the finished product. Furthermore, being free tomove, non-bonded synthetic fibres can be more readily driven by jetsinto the interstices of the reinforcing fabric and thereby improve peelstrength between the webs and the reinforcing fabric. This isparticularly important for hard wearing shoes, and relatively highpercentages of such fibres (compared to bicomponent) can be used withoutover-stiffening the final product.

In the case of a fabric reinforcing material having one or more webs orbodies of fibres united with the fabric, the (or each) web or body maycontain a higher proportion of said further synthetic material adjacentthe reinforcing layer than at the outer surface thereof.

The effect on handle of such further (non-bicomponent) fibres depends ontheir fineness as well as their percentage of mix, and in this respectthey should preferably be not more than 1.7 dtex. For minimum effect onhandle, such fibres can be into the “microfibre” range of well under 1.0dtex, and with sufficiently fine manmade fibres, adequate handle can bemaintained at over 10% of total fibre content. However reducing finenessincreases the number of fibres present, which in itself can change thefeel of the product. Alternatively where Improved peel resistance ismore important than handle, coarser fibres can produce better all roundresults. Generally, for reasons of cost and detracting from theleather-like feel of the final product it is preferable to keep furthersynthetic fibre content to below 20% by weight of the end product sheetmaterial. The range may be 5-20% by weight.

Particularly with coarser manmade fibres, even small percentages in themix can detract from the characteristic surface feel of real leather,particularly as after buffing the superior abrasion resistance ofmanmade fibres can make them more prominent. In a further feature of theinvention, hot air or other suitable heat sources are applied to thesurface of the web after buffing at sufficient temperature to melt backthe bicomponent fibres without adversely affecting the leather fibres.The technique exploits the high moisture retention of leather whichkeeps it cool, and its property of charring rather than melting whensubjected to excess local heat. Any such charring can be brushed orlightly buffed away, leaving a substantially natural leather finish.

BRIEF DESCRIPTION OF DRAWING

The invention will now be described further by way of example only andwith reference to the accompanying drawings in which:

FIG. 1 is a schematic view of initial stages of one form of apparatusused in the performance of the method of the invention and which showsthe main operating principles of a commercially available plant formaking a fibre web with a fused bicomponent network; and

FIG. 2 shows further stages of the apparatus for combining such web withreinforcing fabric and hydroentangling the resulting sandwich.

DETAILED DESCRIPTION

Referring to FIG. 1, waste leather fibres made by textile reclaimingmethods lightly chopped to a maximum length of approximately 6 mm aremixed with 4% of 1.7 dtex bicomponent fibres and 5% of 3.0 dtex standardpolyester fibres both cut to constant 6 mm length. The mixture is evenlydistributed at around 200 g/m2 onto a driven porous belt 1 by at leastone pair of perforated drums 2 while the fibres are drawn onto theporous belt by vacuum box 3.

The resulting web 4 of evenly laid fibres is transferred by aconventional vacuum conveyor 5 to porous belts 6 and 7, which containand partially compress the web while hot air from a box 8 is blownthrough belts 7 and 6 and web 4, and received by a suction box 9. Thetemperature of the hot air is sufficient to melt the outer sheath of thebicomponent fibres (but not the inner core) and thereby fuse the fibrestogether at their intersections.

Before the melted sheaths at the intersections of the bicomponent fibressolidify, the web may be compressed by nip rollers 10 to form a denserweb consisting of un-bonded leather and polyester fibres supported by athree-dimensional network of fused bicomponent fibres. On solidificationof the intersections the network provides sufficient strength for theweb to be wound onto reel 11 for transport and/or storage.

Referring to FIG. 2, two such webs 4 a and 4 b unwind from reels 11 aand 11 b together with fabric reinforcement 4 c from reel 12, and arebrought together by rollers 13 to feed onto a porous belt 14. Webs 4 a,4 b and fabric 4 c comprising a composite web 15 are conveyed by belt 14through hydroentangling jets 16, and water from the jets is drawnthrough web 15 and porous belt 14 by vacuum box 17. Water reboundingfrom the surface of the composite web is collected in trays 18 andconveyed away as described more fully in the prior application.

For complete hydroentanglement the composite web is passed through aplurality of successive hydroentanglement stages, one or more of whichmay incorporate a screen applied over the surface of the web 15.Hydroentanglement stages are arranged so that jets can be applied toboth surfaces of the web, and for the present example, such applicationof jets is on alternate sides through 5 such stages at a speed of 10m/min.

In this example perforated screens with an open area of approximately60% made from chemically etched stainless steel of the type described inthe prior application are applied to each side of the web for the finalstage of hydroentangling in order to mask the furrow marks from thejets. To prevent coincidence lines forming on the surface, the pitch ofthe apertures of the screen is made the same as the pitch of the jetorifices.

Jet orifices for this example are 140 microns at 0.9 mm centres, andwhen applied through the screens, jet pressures can be at the maximumnormally available in commercial hydroentangling equipment at 200 bar.Pressures without the screen may be reduced slightly to 180 bar, andunlike similar webs without a bicomponent network, this same highpressure can be applied at the first stage of hydroentangling withoutthe need for an external screen. The resulting hydroentangled web may befinished by impregnating with emulsified oils, pigments and pigmentfixatives as may be applied to natural leather, followed by drying andbuffing both sides. The side that received three hydroentangling stages(and therefore has a higher degree of entanglement and attachment to thereinforcing fabric) dan then be coated with a leather-like finish byconventional means as used for coating synthetic leather.

The foregoing procedures may be suitable for shoe material, but forun-coated materials such as for clothing suede, web 4 may be on one sideonly of the reinforcing fabric and four hydroentangling stages applied,all onto the side having the web. After buffing and impregnation the webface may be treated with hot air to cause the projecting manmade fibresto melt and the surface brushed to remove any slight charring leaving afinish closely similar to natural leather.

The resulting sheet material is a high quality reconstituted leatherhaving an excellent feel, strength and surface finish.

It is of course to be understood that the invention is not intended tobe restricted to the details of the above embodiment which are describedby way of example only.

Thus, for example, the web may be wet laid, although there can bedisadvantages with this.

As described in the prior patent application, webs can be wet laid bymethods normally used for paper making or by carding if sufficientlylong textile fibres are included to carry the leather fibres through thecarding process. The use of bicomponent fibres which are added or whichmake up the carrier fibres provides a “screen” for hydroentanglingaccording to the present invention. For effective carding, normally over5% of 1.7 decitex carrier fibres of 20 mm or more is needed, and theleather fibres need to be made by textile reclaiming methods to be longenough to avoid excessive ejection of fines. For wet laying, thebicomponent fibres need to be short and the webs dried before fusing.This may not be wholly satisfactory when the next step is to wet thewebs again for hydroentangling, while the disadvantages of cardinginclude slow rates of production and wastage from the ejection of finefibres.

A wide variety of variations are feasible within the scope of thisinvention. Jet orifice size, screen details, production speeds and otherdetails provided in the prior application can broadly apply to thepresent invention. The main departure is the reduced application ofsurface screens, and to ensure good attachment to the reinforcing core,it is often desirable to hydroentangle on alternate sides of the fabricso that fibres are pushed evenly into the interstices of the fabric.Also, due to the stabilising effect of the bicomponent network,pressures can be higher and leather fibres shorter than in the method ofthe prior application.

Product compositions can vary widely and thickness of the web betweenthe final coated surface and the internal reinforcing layer can differsubstantially from the web forming the back layer. For example, insteadof the equal webs implied in the previously described example, the frontone may be 150 g/m2 and contain 15% non-bicomponent synthetic fibres andthe back may be 250 g/m2 and contain 0% of non-bicomponent fibre. Thebicomponent content for both webs, however, may be constant at 4%.

Fibre lengths can be determined largely by the production limitations ofcommercial web laying equipment and, where alternative web layingequipment (such as carding) can handle long manmade fibres, it may notbe necessary to incorporate fabric reinforcement. Also, where jetmarkings are acceptable in the finished product, there may be no needfor surface applied screens. Alternatively, screens may be usedextensively to supplement the internal screens of the bicomponentnetwork, particularly if the latter are very light and the leatherfibres are particularly short.

Hydroentangling speeds can vary widely depending on a whole range ofparameters, including weight per unit area of material beinghydroentangled, open area of fabric reinforcement, jet pressures, jetdiameter, jet spacing, number of passes through the jets, weight ofbicomponent network, type of leather fibre, number of passes usingexternal screens, and open area of screens. Generally lighter webs canbe hydroentangled at faster speeds, and typically 600 g/m2 material mayrequire 6 m/minute while 200 g/m2 may entangle fully at 15 m/min.

The choice of using relatively long waste leather fibres made by textilereclaiming methods or short ones made by milling (such as conventionalhammer or disk milling) can depend on the cost and availability of thedifferent types of waste leather. Milling is cheaper and can use wasteleather shavings, which are usually cheaper than the sheet waste used intextile reclaiming plant. However end product quality can be lower andmore costly manmade fibre additions may be needed to achieve acceptableperformance. Blends of both types of waste fibre can also be used forintermediate quality products.

As with the prior application, the main limitation in weight ofcomposite webs that can be hydroentangled is the onset ofhydroentanglement itself as this reduces permeability to the jets andconstricts further entanglement. Such constriction is far greater withleather fibres than conventional synthetic fibres but, by using themethods of this invention, it is possible to make acceptable product atrelatively high composite web weights of around 600 g/m2. Producingacceptable quality end product at much above this weight is possible butbecomes increasingly difficult. Lighter webs are easier tohydroentangle, and minimum web weights can be set more by limits of webforming accuracy and limited market demand for exceptionally thinleather products.

The inter-relationships between all the foregoing parameters are complexand can vary considerably for different types of end product. An optimumbalance between output rate, cost and finished product performance canbe established by conducting empirical trials within the broad guidanceprovided in this patent application. The bicomponent network andassociated features of the present invention assist considerably inimproving production rate and product quality at lower cost compared tothe methods of the prior application.

1. A reconstituted leather sheet material having a leather-like feel,the reconstituted leather sheet material being formed by a methodcomprising the steps of: evenly distributing and compressing a mixtureof predominantly waste leather base fibres and additional syntheticfibres to form a web, wherein the additional synthetic fibres havemeltable surface layers and the base waste leather fibres compriseleather fibres having fibrillated branches, heating the web to melt thesurface layers of the additional synthetic fibres so as to cause suchfibres to fuse together at intersections to form fused networkintersections within the web mixture, and subjecting the web mixture tosuccessive hydroentanglement stages to entangle the waste leather fibreswith each other while initially constrained by the network, such thatthe increase in tensile strength arising from the hydroentanglement ofthe fibers within the web is greater than the tensile strength of theweb prior to hydroentanglement.
 2. A method of forming a reconstitutedleather sheet material having a leather-like feel, comprising the stepsof: evenly distributing and compressing a mixture of predominantly wasteleather base fibres and additional synthetic fibres to form a web,wherein the additional synthetic fibres have meltable surface layers andthe base waste leather fibres comprise leather fibres having fibrillatedbranches, heating the web to melt the surface layers of the additionalsynthetic fibres so as to cause such fibres to fuse together atintersections to form fused network intersections within the webmixture, and subjecting the web mixture to successive hydroentanglementstages to entangle the waste leather fibres with each other whileinitially constrained by the network, such that the increase in tensilestrength arising from the hydroentanglement of the fibers within the webis greater than the tensile strength of the web prior tohydroentanglement.
 3. The method according to claim 2, wherein the wasteleather base fibres have a maximum fibre length of 6 mm.
 4. The methodaccording to claim 2, wherein at least 90% of the additional syntheticfibres have a maximum fibre length of 10 mm.
 5. The method according toclaim 2, wherein the additional synthetic fibres constitute less thanabout 10% of the weight of the formed sheet material.
 6. The methodaccording to claim 5, wherein the additional synthetic fibres constituteup to about 5% of the weight of the formed sheet material.
 7. The methodaccording to claim 2, wherein the additional synthetic fibres each hasan inner core surrounded by a respective meltable outer surface layerthat is formed by one or more outer layers having a melting point lowerthan the melting point of the inner core.
 8. The method according toclaim 7, wherein the one or more of the outer layers are polyethyleneand the inner core is polyester or polypropylene.
 9. The methodaccording to claim 2, wherein the additional synthetic fibres have adenier in the range of 1.7 to 3.0 dtex.
 10. The method according toclaim 2, wherein the mixture of fibres also includes further syntheticfibres which are not melted to cause fusion together.
 11. The methodaccording to claim 2, wherein the further synthetic fibres have a denierless than 1.0 dtex.
 12. The method according to claim 10, wherein thefurther synthetic fibres comprise less than 20% by weight of thereconstituted leather sheet material.
 13. The method according to claim2, wherein the leather base fibres have lengths of less than 3 mm. 14.The method according to claim 2, wherein the additional synthetic fibresconstitute no more than 2% of the weight of the web.
 15. The methodaccording to claim 2, further comprising a fabric layer, and the leatherfibres are caused to penetrate the fabric layer.
 16. The methodaccording to claim 2, wherein the additional synthetic fibres constitute2 to 10% of the weight of the reconstituted leather sheet materialformed by said method.
 17. The method according to claim 2, wherein thehydroentanglement is performed using hydroentangling jets of liquid inmultiple passes.
 18. The method according to claim 17, furthercomprising using a collection device positioned adjacent thehydroentangling jets and a surface of the web to collect rebound liquidfrom the jets that rebounds off the surface of the web, such collectionoccurring before the liquid falls back onto the surface of the webthereby to minimize the amount of rebound liquid that falls back on thesurface of the web.
 19. The method according to claim 2, wherein theouter meltable surface layers of the additional synthetic fibres aremelted by passing hot air through the web, and the web is held betweenporous belts during passage of the hot air through the web. 20.(canceled)
 21. The reconstituted leather sheet material according toclaim 1, wherein the sheet material includes a front web and a back web,wherein the front web is about 150 g/m2 and contains about 15%non-bicomponent synthetic fibres and the back web may be about 250 g/m2and contain about 0% of non-bicomponent fibre, and wherein thebicomponent content for both webs may be constant at about 4%.